Pollution detection and monitoring has become of utmost importance as environmental issues and the protection and preservation of natural resources has greatly increased in the public awareness. Substantial technical advances have been made in environmental monitoring and control systems. Such systems should be highly sensitive and responsive to minute quantities of a contaminant and should furthermore be capable of identifying a particular contaminant. Moreover, it is highly desirable that such systems be low in cost, easy to use and adapted for use in remote or inaccessible locations.
One of the more common pollutants is volatile organic compounds (VOCs). A common example of contamination of groundwater is from leaks in underground storage tanks used for storing VOCs such as gasoline and other liquid petroleum fuels. Other VOCs such as organic solvents and lubricants are commonly disposed of at hazardous waste sites such as landfills and often find their way as contaminants to groundwater. Early detection of such contaminants would obviously be highly desirable to minimize damage and facilitate restoration of the environment. Selective identification of a particular VOC would also be highly desirable because it could assist in identifying the source of contamination.
Transition metal-containing double complex salts exhibiting "vapochromism, i.e. a change in color or absorbance in the electromagnetic spectrum, such as in the visible portion of the spectrum, induced by vapors of organic compounds having a designated vapor pressure at room temperature, are disclosed in U.S. Pat. No. 4,826,774. These vapochromic compounds undergo reversible color and fluorescence changes in the absence and presence of VOCs. These types of vapor detecting materials have not yet been incorporated in detection devices which are capable of practical use.
U.S. Pat. No. 5,244,813 discloses another approach to detecting organic analytes involving the absorption and partitioning of the analytes for optical determination which makes use of fiber optic sensors utilizing polarity sensitive solvachromic dyes and polymeric materials. U.S. Pat. Nos. 4,846,548 and 4,892,383 disclose fiber optic chemical sensors (FOCS) for detecting the presence of chemical or biological species by measuring changes in the total internal reflection characteristics of the fiber optic element produced by changes in the index of refraction of a clad or layer of a material which reacts with the chemical or biological species. The latter patent discloses a specific embodiment incorporating a reservoir FOCS formed of a modular cell body. U.S. Pat. No. 5,010,776 discloses an environment contamination detection and analyzing system, such as for use with subsurface contaminants, which includes a probe which collects a fluid sample from the medium for determining the presence of a contaminant having a vapor pressure. Pneumatic communication lines are connected to the probe for transporting a fluid sample by a carrier gas to a detector/analyzer for analysis of the contaminant. None of the aforementioned approaches are adapted for the aqueous media detection of VOCs or the selective detection of VOCs in a low cost device which is easily transported.
The present invention addresses the aforementioned limitations of the prior art by providing apparatus for the optical detection of chemical species such as VOCs, VOC aqueous matrix detection, and selective VOC vapor detection.